Electrophotographic photoreceptors employing organic photoconductive materials have conventionally been produced by forming a function-separated type photosensitive layer having a multilayer construction composed of a charge generating layer containing a charge generating material that absorbs visible light to generate charges and a charge transport layer containing a charge transport material that transports the charges. As charge transport materials, various substances having the property of transporting positive holes are known, such as amine compounds, hydrazone compounds, pyrazoline compounds, oxadiazole compounds, stilbene compounds, and carbazole compounds.
In such a function-separated type of electrophotographic photoreceptor, the mechanically strong charge transport layer generally constitutes the upper layer and, hence, where a conventional positive hole transport material is used for the charge transport layer, the photoreceptor is of the negatively charged type. However, preferred are positively charged photoreceptors from the standpoints of preventing ozone generation in corotrons and controlling the electrification of toners in developers. Although an electron transport material is required for making an electrophotographic photoreceptor to be of the positively charged type with the charge transport layer as the upper layer, a sufficiently effective electron transport material has not been known hitherto.